1. Field of Invention
The present invention relates to branched crystalline polypropylene (BCPP) compositions and methods for the preparation of branched crystalline polypropylene compositions.
2. Description of Related Art
Various processes have been proposed for making polypropylene compositions. Such different processes will typically have different variables and parameters, including different monomer compositions, solvents, additives, reaction conditions, catalyst systems, etc. The properties and characteristics of the final product have a great deal to do with the process variables and parameters that are selected, and it has been recognized that small modifications in such variables and parameters can create significant differences in not only the final product, e.g., polymer properties, but also in the effectiveness of the overall process, e.g., catalyst productivity, presence or absence of gel. Background references include U.S. Pat. Nos. 5,571,867, 6,225,432 B1, 6,323,284 B1, 6,121,383, WO 99/29742, WO 00/37514, WO 02/070572, WO 01/58970, EP 0 645 401 A, EP 1 223 191 A, and Synthesis of Long-Chain Branched Propylene Polymers Via Macromonomer Incorporation, Weng et al., MACROMOL. RAPID COMMUN., Vol. 22, No. 18, 1488–1492 (2001).
An ongoing need exists for processes that provide polypropylene with good processability and high melt strength, which is desirable for applications such as thermoforming, foaming, and blow molding. Poor melt strength of polypropylenes shows up as excess sag in sheet extrusion, rapid thinning of walls in parts thermoformed in the melt phase, low draw-down ratios in extrusion coating, poor bubble formation in extrusion foam materials, and relative weakness in large-part blow molding. Thus, it would be highly desirable to produce a polypropylene having enhanced melt strength as well as commercially valuable processability.
Furthermore, a need exists for a relatively straightforward method of preparing polypropylene having desirable properties, particularly a method for making a BCPP that does not require the use of a cross-linking agent, e.g., post-polymerization treatments, or the use of comonomers that have been found to result in undesirable gel formation, such as certain types of diene comonomers. Finally, there is a need for a process demonstrating high catalyst productivity in forming the BCPPs described herein.